BOSTON — Senator Elizabeth Warren on Thursday called on Mayor Pete Buttigieg, a rival for the Democratic presidential nomination, to open his campaign fund-raising events to the news media and to release a full accounting of the wealthy donors who are gathering contributions for him.
The remarks represented a departure from Ms. Warren’s previous unwillingness to publicly chide most of her top-tier primary opponents, and came as Mr. Buttigieg has overtaken Ms. Warren in some polls in Iowa, the first state to hold a nominating contest next year.
“I think that Mayor Pete should open up the doors so that anyone can come in and report on what’s being said,” Ms. Warren told reporters in Boston. “Those doors shouldn’t be closed, and no one should be left to wonder what kind of promises are being made to the people that then pony up big bucks to be in the room.”
Ms. Warren, of Massachusetts, has made skipping the traditional donor circuit a centerpiece of her 2020 message, funding her campaign primarily through small-donor contributions from grass-roots supporters. But she has rarely invoked that strategy to directly question her rivals.
After her speech at a Democratic Party fund-raiser here, Ms. Warren was asked by a reporter about whether Mr. Buttigieg should release more information about his work at McKinsey & Company, the management consulting firm where he spent nearly three years before his time as mayor of South Bend, Ind. She quickly pivoted to his fund-raising.
“It is even more important that candidates expose possible conflicts of interest right now,” she said. “And that means, for example, that the mayor should be releasing who’s on his finance committee, who are the bundlers who are raising big money for him, who he’s given titles to and made promises to.”
Unlike Mr. Buttigieg, former Vice President Joseph R. Biden Jr., another leading candidate, has opened all his fund-raisers this year to a small clutch of reporters. Neither man has released a full list of bundlers, the supporters who solicit large campaign contributions from other donors (though Mr. Buttigieg released a handful of names earlier in the year).
Besides Ms. Warren, Senator Bernie Sanders of Vermont has bypassed raising money from large donors at private events.
Lis Smith, a senior adviser to Mr. Buttigieg, responded to Ms. Warren on Twitter by calling on her to release old tax returns from her years in the private sector.
“If @ewarren wants to have a debate about transparency, she can start by opening up the doors to the decades of tax returns she’s hiding from her work as a corporate lawyer — often defending the types of corporate bad actors she now denounces,” Ms. Smith wrote.
Ms. Warren has released 11 years of tax returns on her website, covering her time in public office. Mr. Buttigieg has said he has asked McKinsey to release him from the nondisclosure agreement that covered his work.
Ms. Warren has also focused criticism in recent weeks on former Mayor Michael R. Bloomberg of New York, who has spent tens of millions of dollars from his multibillion-dollar fortune since entering the Democratic primary. She took out an advertisement on Mr. Bloomberg’s own television network calling out the former mayor by name. And she sat for an interview on Bloomberg Television, saying, “I don’t believe that elections ought to be for sale.”
In Boston on Thursday, Ms. Warren reiterated her attacks on Mr. Bloomberg, saying his candidacy validated her campaign’s theme of battling corruption in politics.
“If campaigns are nothing more than billionaires and people who suck up to billionaires buying tens of millions of dollars of TV ads, then we’re just not going to have any America where everybody gets an opportunity,” she said.